Manufacture of lithopone



J. A. SINGMASTER AND F. G. BREYER.

MANUFACTURE OF LITHOPONE.

APPLICATION FILED DEC. 4, 1919.

Patented Apr. 4, 1922.

' ing on the highly heated bottom of the muflle UNITED STATES- PATENT, OFFICE.

JAMES A. sI'NGriAsTER AND FRANK G. BREYER, or PALMER'ION, PENNSYLVANIA,

ASSIGNORS TO THE NEW JERSEY ZINC COMPANY, OENEW YORK, Y., A 00320- RATION OF NEW JERSEY.

To all whom it may concern: I

Be'itknown that we, J MES A. SINGMAsm1: and FRANK G. BREYER, residing at Palmerton, county of Carbon, State of Pennsylvania, have invented certain new. and use ful Improvements in the Manufacture of Lithopone;- and we-do hereby declare the following to be a full,-clear, and exact description of the invention, such as will encipitate of zinc sulphide and barium sulphate resulting from theinteraction of solutions of .zinc sulphate and barium sulphide is filter-pressed and, after appropriate drying, is heated or muffled and the hot product plunged directly from the heating chamber into cold water. It has heretofore been customary, in actual practice, to carry out themuflling of the raw or crude lithopone in horizontal muflles, and to this end a layer of crude lithopone is charged on to the bottom of the muffle and heated, usually to a dull red heat. In the usual muflling operation, that portion of the lithopone lyis liable to be overheated, while other portions of,the charge may not he 'sufliciently heated. An' attempt is made to avoid the effect of this non-uniformity ofheating bystirring the material from time to time.

This is only a partial remedy, entails the use of skilled labor,'andrin'creases the difliculty-of maintaining the proper atmosphere in the mufile.

The necessity of a proper atmosphere pro; tecting the lithopone from oxidizing influences during the mufiling operation has heretofore been recognized and, in: certain cases. it has been customary 'tq' introduce a neutral or reducing gas, such, for example,

as steam or producer gas, into the muflie, so

as to maintain a neutral or reducing atmosphere above the charge and'prevent' the ingress of. air.

As heretofore generally practiced, the muflling of lithopone has been an intermittent operation. The crude lithopone is charged into the muflle' through a charging Specification of Letters Patent, Application filed December 4, 1919. Serial No. 842,523!- MANUFACTURE or m'rnorom.

Paten ted Apr. 4, 1922.

door, and after the completion of-the muffling the hot product is manually withdrawn from the mufile into a body of cold water, and thereupon a new charge is put into the muflie. During the charging and dischar ing operations, the temperatureof the muf e necessarily falls, and some time is required to bring a' fresh-char e to the desired muffling temperature. 1 oreover, this intermittentoperationis wasteful of heat. In addition, the amount of lithopone which can be effectively treated at one operation is smaller than the cubical capacity of the muflle; or, in other words, the depth-of the charge in the mufile is kept relatively small com ared with the vertical height of the mu e in an attempt to cut ,down as much as possible-.overheatingor"underheating of portions of the material. This means a relatively large space in' the 'muliie above the charge, ,withthe attendant 'difliculties of maintaining non-oxidizing gases therein and excluding'theair therefrom. r

Iii-the copending application of Breyer, Croll and Farber, Serialv No. 327,921, the existence of critical mufliing temperatures for lithopones of given propertiesis, as far as we are aware, recognized for the first time. The vital" importance of controlled and uniform'heating for the-production of such-superior lithopones is, set forth in the application in question, and the present invention contemplates the m'ufiling of litho-' I pone in a uniform andncontrolled manner and, atthe same timeaprovides for practically continuous and automatic operation. Thus, in its principal aspect, the present invention involves feeding-the lithopone, pref-v erably automatically, as, for example, by

gravity, to .-a properly proportioned,;-;velfti-j cally disposed and externallyi heated ream. We have found that-in a v-verticalmuffi'e,

through which the material passes by grai ity with-consequently little or no agitation,

there is a relationship between the crosssection fand length of the mufile employed which-cannot be exceeded without producing non-uniform material. We believe that the carrying of the heat in such a mufile. to

the center of the column is largely due to its being transferred by the rising gases present, in addition to direct conduction.

When the cross-section is unduly increased, we believe that channeling of the gases takes We do not wish to restrict ourselves to this theory, although it seems the plausible explanation for the phenomena we have observed. We do know, however, that the limits of this relationship between crosssection and length are quite close, and have,

an iron tube twenty-five feet long and ten,

whereas a tube 0 for example, found in actual practice that inches in diameter ives a uniform product, g the same length and twelve inches in diameter ives a quite perceptibly non-uniform product p I n the preferred practice of the invention we use a vertical muffle made of iron or other good heat conducting material, ten inches in iameter and twenty-five feet in length, in which the litho one is heated to the desired temperature and for the necessary period of time. This muffle is continuously operated, and is open to the atmosphere at its upper end and projects into a body of cold water at its lower or discharge end. While the charging and discharging operations may be either continuous or intermittent in character, the muffling operation as a whole is continuous.

Within the retort the lithopone is in effect subjected to a two-stage treatment, the first stage being a preheating treatment and the second stage the muflling o eration proper. In the preheating stage, the lithopone is sub jected, at a temperature below the reacting or critical mufiling temperature, to the scavenging action of the gases escaping from the active mufiling zone, and the incoming litho- I pone is thereby dried and freed from entrained air. In the second sta e or mufiling operation proper the preheate lithopone is subjected to a sufficiently high temperature for the necessary period of time to impart to it the desired properties.

In the accompanying drawings,

Fig. 1 is a diagrammatic elevation of a retort furnace adapted for the practice of the invention; and a g Figs. 2 and 3 are detail views of the starwheel discharging device at the lower end of the retort.

Referring now to the drawings, the retortor muffler 5 may conveniently be made of a cylindrical ipe of wrought iron. The diameter and ength of the pipe should be appropriatelv proportioned to insure uniform heating ofthe lithopone for the necessary period of time. We have secured excellentresults with a wrought iron pipe 10 inches in diameter and from 25 to 30 feet in length. The retort 5 is externally heated by the hot gases resulting from the burning fuel, such as coal, on the grate 6. The grate is embodied in a suitable furnace structure 12 of fire-brick, having a fuel charging door 7 and a flue 8 for conducting the hot products of combustion into contact with the retort 5.

'combustiomwhereby these products of combustion, as they emerge from the flue 8, are

more conveniently controlled and maintained at a practically uniform temperature. The pyrometer 11 indicates to the operator any departure from the desired uniform temperature of the hot gases emerging from the flue 8, and permits him to promptly modify the firing conditionsto secure the desired uniform temperature.

The to of the retort is open to permit the escape o gases. In the drawings, we have represented a car or hopper 13 mounted on rails 14 and positioned directly above the open top of the retort 5 for continuously feeding lithopone into the retort. The car .or hopper 13 is filled with lithopone, and

when emptied is replaced by a full car without interrupting the continuity of the muffling operation. 7 The lower end of. the retort rojects into a body of cold water in a suitab e receptacle 15. If desired, water may be continuously supplied to and withdrawn from the receptacle 15 in order to maintain the body of water therein at the desired temperature to effect the sudden cooling of the lithopone discharged from the retort. In the drawings, we have indicated .a star-wheel discharge operatively mounted at the lower end of the retort 5. This star-wheel discharge comprises a rotatably mounted star-wheel 16.having four blades or wings. The shaft of the star-wheel projects through the'base of the furnace structure 12 and is given a uarter turn at predetermined intervals. iach time the star-wheel is turned through a quarter revolution a definite amount of lithopone is discharged from the retort into the body of water in the receptacle '15. In the drawings we have illustrated a gear train 17-18, in which an appropriate number of teeth on one memberv 17 thereof is omitted so as to obtain the desired periodic turning of thestar-wheel. It will of course be understood that various other devices may be employed for actuating the starwheel. Moreover, other instrumentalities and means may be employed for effecting the continuous or periodic dischar e of an appropriate amount of lithopone rom the lower end of the retort 5.

In the normal operation of the apparatus illustrated in the drawings the retort 5 is' filled with the lithopone. The crude litho pone, as it is charged into the top of the retort, is generally in the form of small lumps, and the spaces betwen these lumps or particles of lithopone, during the muflling operation, are filled with the gases evolved from the lithopone at the muflling temperature, so that the lithopone Within the retort during the entire mufliing operation, is surrounded by a non-oxidizing atmosphere composed, for the most part, of hot water vapor. The gases driven off from the lithopone during the mufllingoperation escape through the open top of the retort. The amount of these gases and the design of the retort are such that there is maintained Within the retort, and more especially in the active mufiiing zone thereof, a gaseous pressure slightly greater than atmospheric pressure, whereby the entrance of air into the retort is effectually. and positively prevented.

In the upper part of the retort the incoming lithopone is subjected to the hot gases escaping from the active mufliing zone of the retort. These hot gases serve to dry andpreheat the lithopone, and more particularly they serve to drive off from the incoming lithopone any occluded or entrained air, so that when the lithopone reaches the active mufiling zone practically all of the air entrained in the original raw lithopone has been eliminated. This insures the muffling of the lithopone under the desired non -oX-.

' idizing conditions.- As the result of this preheating stage in our muffiing operation, We

' are'able to feed into the retort a lithopone containing more moisture than has heretofore been good practice in the u ual lithopone muflles. For this reason,when mufliing in accordance with our present invention, the lithopone need not be dried as thoroughly as has heretofore been necessary. After filterpressing, the crude lithopone ordinarily contains about 50% of moisture. It has heretofore been customary to dry the lithopone until its moisture content was reduced to about 1 or 2%. When muffling in accordance with our present invention, it is entirely of discharging and charging of the retort is so proportioned that a period of from about 5 to 10 hours is required forthe lithopone to travel from the top of the retort to the bottom thereof, during which period the lithopone is subjected to a temperature of from about 550 to 800 C.,depending upon the nature of the crude material and the properties desired in the finished product.

The muflled lithopone, as will be understood by thosie skilled in the art, is removed from the water in the receptacle 15 and subjected to further treatment,such as washing, grinding and drying, substantially in accordance with the present practice.

We have found that lithopone, muffled in accordance with the invention, possesses marked superior properties over lithopone heated -in ordinary mufiles in accordance with the heretofore customary practice. .In particular, We have found that lithopone calcined in accordance with the invention is remarkably resistant to deterioration from sunlight. Inother words, the mufliing operation of the invention results in the production of a superior product having improved light-resisting properties.

From the foregoing description it will-be noted that the mufiling of the lithopone, in accordance with the invention, is carried out in a substantially continuous manner. Moreover, by'the method of the invention, the lithopone is in effect subjected to a two-stage mufiling treatment, whereby the incoming lithopone is subjected to a drying and preheating treatment preparatory to the muffiing treatment propen. Furthermore, the drying and preheating treatment is carried out at the expense of the hot gases driven ofl" from the lithopone during the active muffiing treatment, thereby effecting a marked economy in the heat required for drying of the crude lithopone,- as well as in the heat necessary for the active mufliing treatment.

The apparatus illustrated in the accompapanying drawings 'diagrammaticallv represents our preferred construction, but it will, of course, be understood that the apparatus is susceptible of many modifications Within the spirit and scope of the invention. In

principle, the apparatus of the invention comprises a continuously operated--vertical retort or mufiie open at the top for the escape of gases and sealed, when desired, at the bottom to prevent the entrance of air into the retort. Various expedients may be employed for sealing the bottom of the re 'Itort', and likewise the desired opening at the top of the retort may take different forms. With respect to the opening at the top of the retort, it is only'necessary to provide an escape for the gases resulting from the muffling operation at such a rate that within the active mufliing zone of the retortthere is maintained a gaseous pressureslightly in excess of the atmospheric pressure. I

The construction of the retort 5 of metal, such as wrought iron, is of especial advantage in the mufiling of lithopone, since the high heat conductivity of the metal enables an economical use of the available heat'and insures more uniform mufllmg conditions within the retort. If desired, the retort may be of-a slightly tapered cross-sectional area,

* from above downwardly, throughout a part or the whole of its length, whereby the increase in the cross-sectional area of the retort from the top towards the bottom facilitates the progressive passage of the lithopone therethroug The lithopone, in accordance with the improved method of the invention, is progressively passed through the ;,vertically 'disposed-retort, so that the mufi'ling operation ln'its entirety is a substantially continuous operation. The aforementioned relationship between the diameter and length of the retort is an important feature of the invention.

In general, this relationship'between the .di-

ameter and length of the retort must be such as to insure uniform muflling of the lithopone. By uniform mufiling we mean that substantially -no partof the litho one is overheated and that substantially al of the lithopone is ultimately raised to the desired critical mufiling temperature. F or practical reasons, 'we prefer to employ a retort of.

about twenty-five to thirty feet in effective.

length, and with such a length of retort we i 1 and effective lengt find that the diameter of the retort should not exceed about ten inches for the most satisfactory results. Thus, Wehave secured excellent results with a ten-inch wrou ht iron retort whose length within the effective heating chamber was 25 feet; the retort having an over-all length of 30 feet, 3 feet projecting above the heating chamber and 2% feet extending below the heating chamber. However, while these arethe dimensions. which= we now prefer to employ in practice, we wish-"it .to be understood that the principle of the invention is not limited to a retort of these particular dimensions,

since broadly the invention contemplates such a relationshi between the diameter of the vertically disposed retort that substantially every particle of the lithopone is ultimately sub ected to thedesired critical mufiling temperature,

without overheating, durin passage of the lithopone ti .We claim: j 1. The improvement in the-manufacture of lithopone, which comprises progressively the progressive erethrough.

assing the lithopone through an externally heated and vertically disposed retort of good heat conducting material and'of such proportions as to secure uniforrr'iheating of the ithopone in its assage through the retort; substantially as described. i 2. The improvement in the manufacture of lithopone, which comprises progressively eated and vertically disposed cylindrical retort of good heat conducting material of approximately ten inches in diameter and 0 passing the lithopone through an externally in diameter and of from about chamber; substanti rom about twenty-five to about thirty feet in length so as to secure uniform heatof lithopone, which comprises progressively passing the lithopone by gravity through an externally heated chamber in which a non-oxidizing atmosphere of slightly greater pressure than atmospheric pressure ismaintained by the gases driven ofl from the litho-' pone as a result of the mufiling operation,

sealing the chamber at the bottom against the entrance of air, and permitting the escape of ases at the to of the chamber; substantial y as describe I 5. The improvement in the manufacture of lithopone, which comprises mufiling lithopone in a progressivelyoperated vertical retort in a non-oxidizing gaseous atmosphere at a pressure slightly greaterthan atmospheric pressure, sealing the lower end of the retort a ainst the entrance of air, and permitting t e escape of gases at the top of the retort at such a rate as to maintain within the retort a' pressure slightly greater than atmospheric pressure and thereby preventing the entrance of air into the retort; substantially as described.

6. The improvement in the manufacture of lithopone, which comprises subjecting the lithopone in a progressively'operated vertical retort to a tem erature of from about 550 to about 800 in an atmosphere composed exclusively of the gases driven off from the lithopone as a result of the muffling treatment; substantially as described.

'7. The improvement in the manufacture of lithopone, which comprises passing the lithopone by gravity through an externally heated chamber in which a non-oxidizing atmosphere of slightly greater pressure than atmospheric pressure is maintained by the gases driven off from the lithopone as a result of the mufliing treatment, progressively discharging the mufiled product from the bottom of thechamber intoa. bodyof cold water, sealing the bottom of the chamber against the entrance of air, and permitting th e escape of. ases at the top of the fly as described.

. 8. The improvement in the manufacture of lithopone, which comprises progressively mufiling the'lithopone in two-stage operation, in the firststage of which the lithowhich thelithopone is subjected to a muf 'pone is subjected to a dryingand preheat-' 7 .ing treatment and in the second stage of fling temperature of from about 550 to about 800 (1.; substantially as described.

9. The improvement in the manufacture of lithopone, which comprises progressively passing the lithopone by gravity through a heated upright metallic retort of such proportions as to secure uniform heating of the lithopone in its passage through the retort; substantially aS described.

10. The improvement in the manufacture of lithopo-ne, which comprises progressively passing the lithopone through a heated upright tubular retort, the cross sectional area and length of said retort being so proportioned and the heating thereof being so regulated that substantially all of the lithopone is ultimately raised to the desired muffling temperature and no part thereof is overheated; substantially as described.

11. The improvement in the manufacture of lithopone, which comprises progressively passing the lithqpone through a heated upright retort having a diameter not exceeding about twelve inchesand a length of at least twenty-five feet and thereby uniformly heating the lithopone in its passage through the retort.

12. The improvement in the manufacture of lithopone, which comprises progressively passing the lithopone through a heated upright retort having a diameter not exceeding about twelve inches and a length of at least twenty-five feet and so regulating the heating of the retort that substantially all of the 'lithopone is ultimately raised to the desired muflling temperature and no part thereof is overheated in its passage through the retort.

In testimony whereof we affix our signatures.

JAMES A. SINGMASTER. FRANK G. BREYER. 

